The types of rechargeable battery packs for portable electronic products are increasing in terms of different charge capacity and different cell technology or chemistry. Since each particular battery has their optimum charging profile, a method of distinguishing each battery's charging capacity becomes increasingly difficult. Likewise, each battery chemistry has it's own optimum charging "signature" or profile that allows for a safe rapid charge and cut-off to trickle charge or no charge. The need for today's smart or "Universal" charger to inexpensively distinguish the different cell capacities and cell chemistries increases as the variety of batteries in the market continues to grow. An inappropriately charged battery not only diminishes battery life and efficiency, but could also create a severe hazard due to overcharging and overheating.
A battery charger generally cannot determine the charge capacity and battery cell chemistry inexpensively. U.S. Pat. No. 4,006,396 by Bogut discusses an inexpensive universal battery charging scheme which provides an electrical element having a characteristic related to a predetermined charging rate of the battery. The use of the electrical element in '396 requires an additional contact in both the battery housing and charger, thereby reducing the mechanical integrity of the battery and charger housing. Thus, a need for other inexpensive methods of determining charge capacity and other battery characteristics exists that enhances the mechanical integrity of the battery housing and charger housing.